Is cola-stone formation link just an urban legend?

Cleveland-Urologists at Emory University, Atlanta, may or may not have slain an urban myth, but at the very least, the team has given it a sound kick. Cola in moderation does not change urine chemistries significantly, and therefore does not appear to raise the risk of forming stones, the team concluded after comparing cola to deionized water in a randomized, prospective pilot study.

"We cannot say right now that cola is contraindicated in stone disease. But this is just a pilot study. There is more to come," said J.T. Abbott, MD, a resident in the department of urology at the Emory University School of Medicine working with Kenneth Ogan, MD, and colleagues.

The researchers' conclusion, although tentative, contradicts what appears to be standard advice on nearly every Internet site discussing stone disease, whether the discussions are between consumers or medical professionals. The alleged relationship between cola and kidney disease is so common that the Coca-Cola Co., headquartered in Atlanta, has posted the following prominently on its web site: "Soft drinks cause kidney failure. This rumor reports a young mother dying from the failure of both kidneys, due to consuming soft drinks every day at lunch. Our Response: The rumor about the young woman dying in Pertamina Hospital, located in Jakarta, Indonesia, is not true. The Director General of Food and Drug Control within the Indonesia Health Department has investigated this rumor and found it to be false. Coca-Cola does not cause kidney stones."

"It [cola] has a moderate level of oxalates, between 2 to 6 milligrams per serving," Dr Abbott explained.

The oxalate content of the beverage and several case studies about cola overload may be the reason why cautions against cola consumption appear so frequently in patient information about stone disease.

Controlled diet study

In their study, the researchers put 10 individuals (stone formers and non-stone formers) through two, 6-day phases of a highly controlled metabolic diet. The diet was slightly acid-ash and low calcium (400 mg calcium, 800 mg phosphorus, 200 mg magnesium, 100 meq sodium, and 160 mg oxalate). The patients drank 500 cc (about 17 fluid ounces) of cola twice a day. After a 3-week washout period, the diet was repeated, but this time, the individuals ingested 500 cc of deionized water twice a day.

"Everyone had their food given to them and all diets were the same, with the exception that they drank cola in one phase and water in the other," said Dr. Abbott.

Urine specimens were collected on days five and six of each phase. The researchers noted differences in urine chemistry between the two phases, but none reached significance. Cola was associated with a slightly increased urinary oxalate and slightly decreased urinary citrate and magnesium. Urinary pH showed a minimal increase in cola drinkers, while uric acid minimally decreased.

Dr. Abbott explained that the data were very preliminary. The team hopes to collect data on up to 20 individuals and evaluate the data according to those who have and those who do not have a propensity to form stones. Stone formers and non-stone formers were in the first cohort, but the data were not stratified according to their condition.

Were there any ties between the Atlanta-based researchers and the city's huge cola maker?

"Yes, we are a big Coca-Cola town and no, Coca-Cola had nothing to do with this study," Dr. Abbott said with a laugh, indicating that he had been asked the question several times.

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